Cracking feed from lubricating oil stock



v 13, 19159 w, Q MQYER CRACKING FEED FROM LUBRICATING OIL STOCK Filed lJan. 16, 1956 United States Patent CRAC-KING FEED `FRQM LUBRICATING OIL STCK 4William C. Moyer, Port Arthur, Tex., assignor to The y.Texas Company, New York, N. Y., a corporation-of 'Delaware Application January 16, 1956, Serial No. 559,231

2 Claims. (Cl. 208-87) The present invention is directed to a hydrocarbon conversion process. More particularly, it is directed to a method of Arefining petroleum oil fractions to produce catalytic cracking feed stock and a lubricating oil frac tion from a lubricating oil distillate fraction.

According to the process of this invention a crude oil fraction is distilled to obtain a lubricating oil fraction. The aforesaid lubricating oil fraction is extracted with a solvent to separate a lubricating oil fraction of increased viscosity index and an extract mix fraction comprising solvent and extracted oil. The extract mix is cooled, thereby reducing the solubility of the extract in the solvent and forming separated oil and secondary extract mix iphases. The separated oil is withdrawn and after removal of dissolved solvent is charged to a catalytic -crackingpprocess to effect conversion thereof to useful products.

vSolvent-extraction is a--well-known Vprocess by which lubricating oilfractions-may be refined to producelubricating olli-fractions of increased-viscosity index. Inthis process alsuperior lubricating oil fraction is produced 1as raffinate and anoil of lower qualityis-produced as extract. Likewise solvent extraction is a well-known process by which cracking feed stocks maybertreated .to extract aromatic and asphaltic'constituents. By solventextraction, a superior catalytic crackingfeedstock is1 produced as Vramnate and the extract is disposed of as heavyy fuel oil.

ln the processing of lubricating-oil fractions by solvent extraction, economic considerations `require Vthat ythe extract be'disposed of so as to utilize its greatest value. rihe ,extractfmay be-,ernployed in limited quantities for lubricating; applications Qwhich do notV require higher quality'oils kbut the requirements for such lubricating oils arefrelativelysmall. Lubricating oil extracts'may also be used` asl thermal cracking charge'stock. However, the qualityof'motor fuel produced by;therrnal cracking is poor and is far `below the quality required for modern premium grade motor'fuels. Lubricating oil extracts, in the alternative, may be blended inheavy fuel oils which are of relativelyllow'value.

lln general, extract from solvent refining of'lubricating oilis unsuitable for catalytic cracking feedstock. As pointed out above, when solvent refining is applied to catalyticcracking stocks, the improved catalytic cracking stock isproducedas rainate and the components of poor cracking quality are lconcentrated in the extract. In generaL'the extract from the solvent refining of lubricating oilfractions or catalytic cracking feed stocksis relatively -rich in aromatic components and has a high carbon residue. These extracts exhibit poor cracking susceptibility and result in the production of inordinatelylarge amounts @of carbon. .High carbon yields in catalytic cracking tend tolimit the amount of oil'vvhich may be processed in a given catalytic cracking installationsince the carbon producedis deposited on theacatalyst and must be removed Ibyregenerationf'or burning. lIn addition; these. :extracts -v vhenfcatalytically t cracked produce Patented Jan. 13, 1 959 ICC relatively poor yieldsy of the more .valuableeproducta yfor example, gasoline, and higher yields of less valuable products, f-or example, fuel gas and carbon.

An exception to the 4generalization `that solventextracts of lubricatingv oil fractionsv are poor catalytic cracking feed stocks is found in the extract-,from the solvent rening of light lubricating oil fractions, for example, light lubricating oil fractions having viscosities rangingup `to yabout 55 Saybolt Universal seconds at 210 `F. The extract from the solvent retiningyofsuch oils has x been found to have a carbonresidue of less than 1,0. These stocks may be included inA catalytic cracking feedstock without the production of llarge amounts of carbon. However, the extract nfrom such ,lightlubricating ioil fractions comprise only aminor Vproportion of the-,byproduct extracts produced When a full vrange of all lubricating oil grades are manufactured. The extracts from the remaining heavier oils havebeen found to have carbon residues greater thanl and produce inordinately high yields of carbon when subjected to catalytic cracking as described above.

l have found that an oil of satisfactory -catalytic cracking characteristics may be vseparated from ythe extract produced in the solvent refining of heavytlubricating` oil fractions by coolingthe solvent and extract mixto separate an intermediate extract oil. By the lprocess of'this invention, a lubricating oil ,fraction is Isolventextracted to produce a lubricating oil' ofgimproved viscosity index, the solvent and dissolved extract, referred to as extract mix, from the solvent extraction step is cooled ,tof effect the separation of an intermediate oil `having suitable catalytic cracking characteristics and the remaining extract mix, referred to as secondary extract mix, is stripped to separate solvent and a heavy extract suitable for use as thermal cracking charge stock or for fuel blending. Increased yields of intermediate separated loilpmay'gbe produced by recycling heavy extract in admixture with the extract mix from the solvent refining step. Separated 'oils-suitable rfor catalytic cracking may be produced by the process yof this invention from solvent extracts of both distillate and residuum type lubricatingoilfractions.

In the solvent refining step of the process of thisginvention, solvents are used which have a preferential selectivity for the more aromatic type of `hydrocarbons as compared Withthe -paraflinic type hydrocarbons :pres-` ent in lubricating oil fractions.` Suchqsolvents ,are,;-for example, furfural, phenols, sulfur dioxide,gnitrobenzine, aniline, cresols, chlorex, dimethylformamide, .fjdipropionitriles, ammonia, amines,-etc. Thefsolventsyrnayybe used individually or in mixtures and the solvent .power may bemodified by the addition ofother-components, for example, Water, alcohols, esters andy the; like. :Operating conditions, of course, depend uponthespecic solvent employed but usually employ temperatures;infthe'range of about -40 to 250 F., andvsolvent ratios of about' 0.4 to l0 volumes of solventper volumeof foil. flnihe separation step of the process of this invention, thesolvent extract mix is cooled 10 F. or morefrom the temperature employed in the solvent extraction step and, suitably to a temperature Within the range of about l0to.l00,li. belowthe temperature of the solvent extraction istep. The Vtemperature of the intermediate vseparation lstep may, therefore, vary over a- Wide-range butwill; always be lower than the temperature'of the solvent refining step. The greater the differential -betweenjtherefiningV step and the separating step, the greater Will be thegyield of separated4v oil. The lower thel differentialtemperature, the lower is the aromatic-contentand carbon residuepf the separated oil and the'higher isthe qualityf offithe separated oil for catalyticv cracking. They temperature of the separation step may, therefore, I. ,be f controllegdfgtoj produce precisely` the, v.qualitywoff catalytic cracking sfeed stock desired. Further, the integrationof solvent rening with catalytic cracking permits greater exibility in the solvent refining step. When so integrated, conditions may be altered to increase the throughput of the solvent extraction tower to achieve increased production of high viscosity index lubricating oils without the losses accompanying the lowered selectivity which would otherwise follow. Changes in conditions which reduce selectivity in the solvent refining step of the process of this invention result in the production of increased quantities of valuable catalytic cracking feed stock.

An advantage of the process of this invention is that hydrocarbon oils suitable for catalytic cracking charge stock may be produced from the extract obtained in the solvent refining of lubricating oils.

Another advantage of this process is that solvent relining of lubricating oils and catalytic cracking of a solvent refining extract fraction may be integrated to obtain products of greatest value.

Another advantage of the process of this invention is that it results in the production of high quality lubricating oils and high quality motor fuel fractions and less low value fuel oil.

Another advantage of the process of this invention is that greater flexibility of operating conditions and increased lubricating oil production in a solvent refining process are permissable since losses of oil into extract fractions due to reduced selectivity may be recovered in the form of increased production of high quality catalytic cracking feed stock.

The accompanying drawing diagrammatically illustrates one embodiment of the process of this invention. Although the drawing illustrates one arrangement of apparatus in which the process of this invention may be practiced, it is not intended to limit the invention to the particular apparatus or material described.

y Reduced crude oil from an external source, not shown, is charged through line 1 to vacuum tower 2 Where it is subjected to distillation at subatrnospheric pressure to separate gas oil, lubricating oil, and residuum fractions. Although the drawing shows the separation of only a single lubricating oil fraction, it is, of course, possible to separate several fractions at intermediate points in the vacuum tower to produce stocks having varying viscosity ranges. Any or all of the lubricating fractions thus produced maybe employed in the process of this invention.

The residuum fraction is withdrawn from the vacuum tower through line 3 and is discharged to external storage or use not shown. This residuum may be employed in further processing to prepare lubricating oil fractions, catalytic cracking feed stock fractions or fuel components. For example, the vacuum residuum may be subjected to deasphalting with propane to produce lubricating oils or catalytic cracking feed stocks. The asphalt separated from the residuum may be blended with catalytic cracked cycle gas oil to produce useful fuel blends.

Vacuum gas oil is removed from the vacuum tower through line 4 to external use or storage, not shown. The vacuum gas oil is an excellent catalytic cracking feed stock and may be converted by that process to high quality motor fuel fractions and fuel oil components. A lubricating oil fraction is withdrawn from the Vacuum tower through line 5 and charged to a solvent extraction tower 6. In the solvent extraction tower, the lubricating oil fraction is contacted with a solvent, e. g., furfural, which removes the more aromatic hydrocarbon constituents of the oil. The solvent is introduced through line 7 and flows countercurrent to the oil through the tower.

Rainate, the lubricating oil fraction from which the more aromatic constituents have |been removed, is withdrawn through line 8 and directed to external storage or further processing not shown. This fraction has a higher viscosity index than the lubricating oil fraction charged to the solvent extraction tower .and is useful in the manufacture of high quality lubricating oil products. Extract mix comprising the more aromatic constituents dissolved in the solvent is withdrawn from the bottom of the tower through line 9. The operation of the solvent tower has been described with reference to a system in which the solvent is heavier than the lubricating oil fraction being treated. When the solvent is lighter than the oil treated, the solvent is introduced at the bottom of the tower, the oil is introduced at the top, extract mix is withdrawn from the top and ranate from the bottom of the tower. When furfural is used as solvent, the solvent extraction 4tower is operated at a lower bottom temperature range of about 100 F. to 200 F. with solvent rates of about 0.75 to 4.0 volumes of solvent per volume of oil.

Extract mix in line 9 is passed through -cooler 10, to cool the extract mix to about to 100 F. The cooled extract mix is then passed through line 9a to separator 11. In separator 11, an oil phase separates from a secondary extract mix phase. The separated oil is withdrawn through line 11a and is charged to solvent stripper 12. Solvent stripper 12 is a fractional distillation means employed to separate a relatively small amount of solvent which is dissolved in the separated oil. in the case Where furfural is employed as solvent, the separated oil may contain about 3 to 8 percent furfural. Solvent is withdrawn from the solvent stripper through line 12a and is discharged for further use not shown. Stripped separated `oil is withdrawn through line 13 for use as catalytic cracking feed.

'In the ligure, the catalytic cracking process shown is that commonly known as uid catalytic cracking. However, other types of catalytic cracking may also be used in the process of this invention, for example, xed bed catalytic cracking, fluidized fixed bed catalytic cracking, and moving bed catalytic cracking. The solvent free separated oil in line 13 is combined with gas oil cracking stock from line 14 and the combined feed charged to the cracking unit through line 15. The combined feed is co-mingled with hot catalyst from line 16 and the catalyst and oil is passed through line 17 and distributing cone 18 into catalytic cracking reactor 19. Cracked products comprising gases, high quality motor fuel fractions, gas oils and fuel oil components are withdrawn through cyclone separator 20 and line 21 to external separation and further processing not shown. Catalyst from the catalytic cracking reactor and coke deposited thereon are withdrawn through standpipe 22 and carried by means of an air stream from line 23 through line 24 and distributing cone 2S into the catalyst regenerator 26. Coke is burned oif the catalyst in the generator 26 and flue gases pass through cyclone separator 27 and are discharged through line 28. Hot regenerated catalyst is withdrawn from the regenerator 26 through standpipe 16 for reuse in `the process.

Secondary extract mix from separator 11 is withdrawn through line 29 and passed to solvent stripper 30. Solvent stripper 30 is a fractional distillation means employed to separate the solvent from the extract oil. Solvent is withdrawn from the solvent stripper through line 31 and is discharged for further use, not shown. The s-olvent may be, for example, returned to the solvent extraction tower. Extract from the solvent stripper is withdrawn through line 32 and discharged to externalstorage and utilization not shown. The extract may be employed as thermal cracking feed stock, or it may be blended with other components to manufacture marketable fuel oils. Alternatively, a portion of the extract may be recycled through line 33 and combined with the extract mix from the solvent extraction tower in line 9 in order to increase the yield of separated oil in separator 12.

The process of the invention may be more fully understood by reference to the following example which is illustrative of one embodiment of this invention.

A lubricating oil fraction having a gravity of 22.0

API, viscosity of 84 Saybolt Universal seconds at 210 F. and viscosity index of 80 is solvent reiined with furfural as described above at a tower bottom temperature of 165 F. and a solvent to oil ratio of 2.25 to 1. A refined oil is produced as rainate having a gravity of 28.5 API, a viscosity of 68 Saybolt Universal seconds at 210 F. and a viscosity index of 101. Concornitantly an extract mix is produced comprising 26 percent of the oil charged to the solvent refining tower and furfural. When this extract mix is stripped without intermediate separation of oil, an extract is produced having a gravity of 12.0, viscosity of 406 Saybolt Universal seconds at 210 F., a carbon residue of 4.91 and a sulfur content of 0.86 weight percent. This extract is unsuitable for catalytic cracking feed stock because of the high carbon residue.

lThe extract mix above is cooled to 95 F.; an oil layer comprising about 42 percent of the total extract is separated from a secondary extract mix. This separated oil has a gravity of 21.2 API, a viscosity of 107 Saybolt Universal seconds at 210 F., a carbon residue of 0.63 weight percent and a sulfur content of 0.49 weight percent. This separated oil is charged to a uid catalytic cracking unit operating at a temperature of 920 F., a space velocity of 2.0`pounds of oil per hour per pound of catalyst and with a catalyst to oil ratio of 1.0. In comparison with a virgin gas oil cracking feed stock, the separated l oil is found to be characterized by high catalytic cracking susceptibility, and at a given conversion level, by low yields of fuel gas, high yields `of motor fuel fractions and the same yield of carbon. The separated oil produced by the process of this invention is thereby shown to be a superior catalytic cracking feed stock.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and only such limitations should be imposed as are indicated in the appended claims.

I claim:

l. The process that comprises distilling a crude oil fraction to separate a lubricating oil fraction having a viscosity above about 55 Saybolt Universal seconds at 210 F., subjecting said lubricating oil yfraction to solvent extraction in the presence of furfural at a tower bottom temperature of about 100 to 200 F. and at a solvent rate of about 0.75 to 4.0 volumes of solvent per volume of oil to separate a lubricating oil fraction of increased viscosity index as rainate and an extract mix comprising furfural and dissolved extract, cooling said extract mix to a temperature of about 10 to 100 F. below the temperature of said solvent extraction such that an oil phase having a carbon residue when freed of solvent of less than 1.0 weight percent and secondary extract mix phases are formed, separating said oil phase, separating dissolved solvent from said separated oil phase and charging at least a portion of said solvent free 'separated oil to a catalytic cracking process to eect conversion of said solvent free separated oil to lower boiling products.

2. The process that comprises subjecting a lubricating -oil fraction having a viscosity above about Saybolt Universal seconds at 210 F. to solvent extraction to separate a lubricating oil fraction of increased viscosity index as railinate and an extract mix comprising solvent and extract, cooling said extract mix to a temperature within the range of about 10 to 100 F. below the temperature of said solvent extraction and such that an oil phase having a carbon residue when freed of solvent of less than 1.0 weight percent and a secondary extract mix phase are formed, separating said oil phase, separating dissolved solvent from said separated oil phase, charging at least a portion of said solvent free separated oil to a catalytic cracking process to etect conversion of said solvent free separated oil to lower boiling products, separating said secondary extract mix into a solvent fraction and an extract fraction, and recycling at least a portion of said extract in admixture with said extract mix.

References Cited in the file of this patent UNITED STATESA PATENTS 2,203,930 Smith June 11, 1940 2,374,102 Jahn et al. Apr. 17, 1945 2,748,055 Payne May 29, 1956 

1. THE PROCESS THAT COMPRISES DISTILLING A CRUDE OIL FRACTION TO SEPARATE A LUBRICATING OIL FRACTION HAVING A VISCOSITY ABOVE ABOUT 55 SAYBOLT UNIVERSAL SECONDS AT 210* F., SUBJECTING SAID LUBRICATING OIL FRACTION TO SOLVENT EXTRACTION IN THE PRESENCE OF FURFURAL AT A TOWER BOTTOM TEMPERATURE OF ABOUT 100 TO 200* F. AND AT A SOLVENT RATE OF ABOUT 0.75 TO 4.0 VOLUMES OF SOLVENT PER VOLUME OF OIL TO SEPARATE A LUBRICATING OIL FRACTION OF INCREASED VISCOSITY INDEX AS RAFFINATE AND AN EXTRACT MIX COMPRISING FURFURAL AND DISSOLVED EXTRACT, COOLING SAID EXTRACT MIX TO A TEMPERATURE OF ABOUT 10 TO 100* F. BELOW THE TEMPERATURE OF SAID SOLVENT EXTRACTION SUCH THAT AN OIL PHASE HAVING A CARBON RESIDUE WHEN FREED OF SOLVENT OF LESS THAN 1.0 WEIGHT PERCENT AND SECONDARY EXTRACT MIX PHASES ARE FORMED, SEPARATING SAID OIL PHASE, SEPARATING DISSOLVED SOLVENT FROM SAID SEPARATED OIL PHASE AND CHARGING AT LEAST A PORTION OF SAID SOLVENT FREE SEPARATED OIL TO A 